POLYMERS　Vol.70　No.2
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COVER STORY
Moderate Balance of “Precision” in Design of Polymers
COVER STORY: Highlight Reviews
Molecular Weight Distribution and Block Polymer Self-Assembly Nathaniel A. LYND, Mahesh K. MAHANTHAPPA, and Atsushi NORO
<Abstract> Complementary theories and experiments have revealed how molecular weight distribution breadth impacts microdomain sizes, composition-dependent phase boundaries, and order state stabilities of block polymer soft materials. Recent developments in precision syntheses of discrete block polymers and those with controlled molecular weight distribution shapes promise deeper insights into the self-assembly of disperse inhomogeneous block polymers and greater control over their properties and applications.
Keywords: Morphology / Mesoscopic Phase Separation / Segment Dispersity / Order-Disorder Transition (ODT) / Skewness
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Manipulation of Backbone Orientation in Semiconducting Polymers Itaru OSAKA
<Abstract> Molecular orientation is essential for organic materials. In the area of organic electronics, orientation of semiconducting polymers plays a crucial role in determining the charge transport property and thereby the device performances. Questions that arise here are how to control the orientation and how to utilize the orientation motifs to maximize the device performances. Herein, I will show that the primary structures of the polymers greatly affect the orientation of the backbone in the self-assembled structure. In particular, design of the side chain is critical for controlling the backbone orientation. Further, it is found that the distribution of orientation in the film is important for understanding and thus improving the device performances.
Keywords: Semiconducting Polymers / π-Conjugated Polymers / Orientation / Intermolecular Interaction / Organic Field-Effect Transistors / Organic Photovoltaics / Charge Transport
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Development of Superabsorbent Polymers with Moderately Controlled Structures Using Iodine Transfer Polymerization Toru MIYAJIMA
<Abstract> We succeeded in developing a novel class of acrylic acid （AA）-based superabsorbent polymers （SAPs） with remarkably improved absorption performance by applying iodine transfer polymerization （ITP）. A specific organoiodine chain transfer agent was newly developed and found to provide moderate to good control over the polymerization of AA in aqueous solution. Dynamic light scattering （DLS） measurements revealed that the polymer network prepared using our ITP technology is relatively homogeneous. Our new SAP exhibits a good balance between absorption capacity and gel strength, and it enables a quick response to diversified customer needs in the diaper industry. To the best of our knowledge, this work is the first case in which reversible-deactivation radical polymerization （RDRP） has been practically applied to commodity polymer products. This review focuses on how we connected the old but highly practical ITP and SAP production.
Keywords: Superabsorbent Polymer / Iodine Transfer Polymerization / Gel / Controlled Polymerization
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COVER STORY: Topics and Products
Functions of Vitrimers Provided by Cross-Linked Structures with “Associative” Bond-Exchange Mechanism Mikihiro HAYASHI
<Abstract> Vitrimers are a new class of cross-linked materials, which have been recently invented to solve the problem of conventional cross-linked materials such as, poor recyclability and healability. In this article, fundamental characteristics and physical properties of vitrimers are demonstrated. In vitrimer networks, the bond-exchange occurs without distinct separated steps of bond dissociation and re-association, and such exchange mechanism is nowadays referred to as “associative” dynamic bond exchange. During the bond-exchange, the network topology is constantly altered with keeping the network integrity and constant cross-link density, which is the biggest uniqueness for vitrimer networks. Owing to the above nature, vitrimers show some useful functions that cannot be attained in thermoplastic and thermosetting polymers. Among various functions, re-processability without sudden flow at high temperatures is an outstanding function of vitrimers. This is enabled by the very gentle temperature dependence of viscosity change, which is described by an Arrhenius-type relationship, unlike the WLF-type relationship for thermoplastics.
Keywords: Associative Dynamic Covalent Bond / Vitrimer / Cross-Linked Material / Network Topology Alternation
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Two-Dimensional Films of Organic Semiconductors Realized Through Layer-Number Controlling Technique Shunto ARAI
<Abstract> We have developed a unique solution-based technology to form ultrathin two-dimensional organic-semiconductor layers with single-molecular bilayer thickness. A new concept, geometrical frustration, was adopted to suppress multilayer crystallization, while maintaining intralayer molecular ordering, using an extended π-conjugated framework （πCore） asymmetrically substituted by an alkyl chain （πCore-Cn）. Blade-coating with a solution containing two kinds of πCore-Cns with different alkyl-chain lengths yields single-molecular bilayers （SMBs）. The uniformity and size of fabricated SMBs are unprecedented compared to other self-assembly processes. The obtained SMBs afford organic thin-film transistors （TFTs） showing excellent device characteristics with high carrier mobility and low-voltage operation below 2 V. Additionally, the obtained TFTs also exhibit highly sharp on/off switching behavior characterized by the slope of drain current curve in subthreshold regime, which is close to the value of the theoretical limit known for general TFTs. This finding should pave the way for SMB-based ultrathin and super-flexible electronics.
Keywords: Self-Assembly / Molecular Bilayer / Organic Semiconductor / Printed Electronics / Organic Thin Film Transistors
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Surface Structure of Insects: Irregularities and Functions Shinya YOSHIOKA
<Abstract> Some insects have submicron-sized structures on their surface. One example is the array of protrusions that can be found on the compound eye of moths and the wings of some cicadas. This kind of structure is called moth-eye structure or nano-pile structure and is known to have several functions such as anti-reflection, high water-repellancy, and a function preventing other insects from walking on. It is quite interesting that those functions are realized despite the structural irregularities; the height of the protrusions are not uniform but distributed and the lateral arrangements are far from the regular hexagonal array. This article reports a study on the relation between the structural irregularities and functions. Theoretical calculation and experiments revealed that the anti-reflection is robust to the structural irregularities.
Keywords: Moth Eye Structure / Biomimetics / Surface Structure
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Polymer Science and I: A Personal Account
#I’ll Figure it Out Shotaro HAYASHI
<Abstract> There are times when I’m spending my future without feeling a sense of crisis. You and I may not be confident in yourself or maybe afraid to fail. Still, I was positive about what I liked and always want to say “I’ll figure it out （nantokasuru）”.
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Front-Line Polymer Science
Fine Synthesis and Functionalities of One-dimensional Polymers with Well-defined Threading Structures Hiroshi MASAI, Jun TERAO
<Abstract> Finely synthesized macromolecules have gained importance as their structures and functionalities can be tuned by precise engineering. Desired properties and functionalities have been imparted by controlling the nanoscale structures of such macromolecules. In particular, compounds with interlocked structures, such as rotaxanes and catenanes, have attracted attention because of their unique supramolecular structures. In such supramolecular structures, the mobility and freedom of the macrocycles are restricted on the axle and dependent on other macrocycles, imparting unique functionalities to the threading structures. Recently, the ultrafine engineering and the functionalities of threading structures have been reported for the development of synthetic methodologies of “defined” threading structures, based on the number and position of the cyclic molecules, which are not dispersed on the axle. Herein, we review the effective synthetic methodologies of one-dimensional polymers bearing threading structures and on functionalities derived from precise engineering by discussing the latest reports and trends.
Keywords: Supramolecular Chemistry / Rotaxane / Host-Guest Chemistry / Fine Synthesis
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